Cathode-ray oscillograph control



Dem 1929. E. J. WADE ET AL CATHODE RAY OSCILLOGRAPH CONTROL Filed Jan.26, 1929 Inventors: Elmer.J.Wa.de; William .JiRudgeJ'vg 8 TheirAttorney.

Patented Dec. 3, 1929 UNITED STATES ELMER J. WADE AND WILLIAM J. RUDGE,

PATENT OFFICE JR., OF PITTSFIELIJ, MASSACHUSETTS, AS-

SIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORKOATHODE-RAY OSCILLOGRAPH CONTROL Application filed January 26, 1929.Serial No. 335,368.

Our invention relates to control apparatus for cathode ray oscillographsand other voltage responsive devices and its primary object is toprovide automatic means for setting into operation a cathode rayoscillograph on the occurrence of a transient condition such as a strokeof lightning in time for the oscillograph to record such condition. Theinvention may have other applications and may be used generally-as ahigh speed relay device.

In the study of the effect of lightning on electric power lines it isdesirable to obtain a record of the magnitude, duration and character ofthe surge resulting therefrom. The cathode ray oscillograph is aninstrument capable of recording phenomena of lightning rapidity, once itis in operation. Generally, the transmission line on which theinvestigation is to be made is energized and the actuating circuits ofthe cathode ray oscillograph must be devised to prevent the normal linevoltage from interfering with the measuring circuit. Also, the time lagof the measuring circuit must be reduced or the transient surge must bedelayed in its influence on the oscillograph until the latter is inoperating condition to record the surge. The surge may be positive, ornegative, or oscillatory. These, and other considerations, make itsomewhat difficult to successfully record lightning and other analogoussurges occurring on live transmission lines and the controllingarrangement described below has been developed to provide self-actuatingautomatic apparatus capable of recording surges of steep wave front andshort duration as they occur on live transmission lines. The apparatuscan obviously be used on transmission lines which are not energized aswell as for general surge testing purposes.

The features of our invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto.

For a better understanding of the invention reference is made in thefollowing description to the accompanying drawing which shows in Fig. 1one arrangement of the circuit and essential auxiliary apparatusembodying the invention as connected to control a cathode rayoscillograph in response to surges on a live transmission line, and Fig.2 is a reproduction of a lightning surge record obtained by thisapparatus on a power line in the State of Pennsylvania.

Referring to the drawing, 10 represents one phase of a high voltagetransmission line. 11 designates a cathode ray oscillograph thecathodeof which is represented at 12 and the anode at 13. 14 representsa tubular aperture through which a ortion of the cathode rays passdownward etween the sweep circuit plates 15 and the deflection plates 16to the recording film represented at 17.

During the normal condition of line 10 it is generally desirable that nocathode rays shall be given off from the cathode 12. The essentialproblem involved is then to start the oscillograph into operation inresponse to an abnormal surge on the transmission line in time for thesurge to be recorded on film 17. This requires an abrupt excitation ofthe cathode for initiating the cathode rays on the occurrence of atransient voltage, the simultaneous excitation of the sweeping plates 15at a rate which will move the cathode ray across the film to give asatisfactory time axis and the energization of the deflection plates 16in response to the voltage surge to be recorded so as to move therecording rays at right angles to the sweeping motion produced by plates15. The explanation of how these functions are accomplished will betaken up and explained in the order mentioned above.

An auxiliary source of supply is provided for exciting the cathode, asfollows: Connected across the cathode and anode or between cathode andground through a high potential direct current source of supply arecondensers 19 and 20. The direct current source comprises rectifyingtubes or kenotrons 21 and 22 supplied through a transformer 23 from analternating current source 24. The arrangement is such as to produce apredetermined negative voltage at the cathode 12 with respect to ground.Regulating means, such as an induction regulator 25, is preferablyprovided to regulate the charging voltage of the condensers 19 and 20.Connected in series with the direct current portion of the condenserdischarging circuit v of the condensers.

that there will exist across spheres 26and 27 a high direct currentpotential, for example,

from 50,000 to 100,000 volts. The sphere gap is adjusted so that thisvoltage is insufiicient to break down the gap through the intermediatesphere 28 under normal conditions. Sphere 28 is normally energizedthrough the grounded capacitance connection 29 at a potential gradientwhich is about midway 7 tween the potentials impressed upon spheres 26and 27. The connection 29 may comprise an insulator strin of suflicientlength to withstand a lightmng surge without arcing over and ofsufiicient capacitance to enable the sphere 28 to become charged by anypotential on the transmission line.

Under the conditions specified, whenever a positive or a negative surgeoccurs on line 10, the potential of the intermediate sphere 28 will beraised or lowered sufficiently to initiate a breakdown between it andone of the spheres 26 or 27. This simultaneously starts a discharge ofthe condensers 19 and 20 between spheres 26 and 27 and immediatelyraiscs the voltage between cathode 12 and the grounded anode sothatcathode rays are produced in the oscillograph tube. The

' charge on the condensers 19 and 20 which is released on the sphere gapside by the discharge across the sphere gap releases a correspondingcharge on the oscillograph side,

The resistance 30 is too high to dissipate instantaneously this releasedcharge and as a consequence'it produces the required excitation of thecathode and cathode rays are produced in the oscillo raph tube. I

' itesistances 40 are desirable to limit the charging-rate of thecondensers and thus prevent injury to the kenotrons during the sharpfocus of the recording ray. The value" initial charging period.Resistances 41 are desirable to prevent excessive oscillations in thecondenser circuit when the breakdown of the sphere gap'occurs. Otherwisewe may have suificient fluctuation of the cathode ray exciting voltageto prevent the desirable of the resistance 30 will depend somewhat onthe capacitance of the condensers 19 and 20. The condensers should havesuflicient capacity to maintaina I steady discharge through theresistance 30 and the oscillograph tube long enough to recordthetransient under investigation; for example, a duration of 100microseconds orlonger. The resistor 30'may have from 30,000 to 100,000ohms resistance and the capacitance of condensers 19 and 20 may be fromone-fourth to one micro;

farad capacity each with satisfactory results.

The cathode ray is produced in less than one one-millionth of a secondafter the start of a surge which initiates a breakdown of the spheregaps and continues to be produced long enough to record lightningsurgesof ordinary duration. As soon as the normal line voltage conditionsareagain established and the condensers 19 and 20 are discharged the arcacross the sphere gap and the cathode ray cease and the condensers 19and 20 are again recharged. As soon as the film is changed theapparatus-isready for another operation. I

The electrostatic field across plates 15 employed for sweeping thecathode ray across the film ata suitablerate to provide a satisfactorytime axis is also supplied from the discharge of condensers 19 and 20.The discharge voltage is applied across a series resistance 31 and acondenser 32 so proportioned that thecondenser voltage varies at a raterequired to give the proper sweeping time to the cathode ra as it passesbetween plates 15. A kenetron tub series with the condenser 32 toprevent the return of the ray to the film after the transient has beenrecorded and while the condensers 19 and 20 are still discharging.- Aparallel sphere gap 3a is provided to limit the sweep plate voltage to avalue below the plate flashover voltage. .-A high resistance leak 35 ispreferably connected across the condenser 32 to maintain the sweepingplates at ground potential prior to the occurrence of a surge. Theresistance 42 is desirable to prevent oscillations of the sweep platevoltage.

The transmission line transient voltage i applied to the deflectionplate 16 through the ad ustable condenser 37 and capacitancepotentiometer 38. The latter reduces the 'volt age across the deflectionplates .16 to a value applicable to the oscillograph and the condenser37 serves as adjustable means to give a satisfactory scale deflection ofthe cathode ray when the surge voltage is impressed. The capacitancepotentiometer 38 1S preferably grounded as shown to permit suflicientleakage therethrough to prevent a bound charge from accumulating.Resistance 39 is for the same purpose.

We may visualize what happens when a lightning surge occurs on thetransmission line by reference to Fig. 2 which represents a record of alightning surge obtained by means of the apparatusdescribed. Prior to alightning surge the apparatus is adjusted so that the recording ray, ifit were produced, would be focused at a point represented at a point A.A stroke of lightning on line 10 sets the apparatus into operation, aspreviously described. The record at the beginning Of the transient isnot very distinct, it being somewhat blurred, as represented at B, owingceased and the straight line record to the right of this pointcorresponds to the normal line voltage and the path of the ray as it isswept off the film by the plates 15. By suitable calibration of theapparatus, the duration and magnitude of the transient may bedetermined. This particular lightning surge reaches its maximum value inabout 5 microseconds and lasted about micro-seconds.

In accordance with the provisions of the patent statutes we havedescribed the principle of operation of our invention together with theapparatus which we now consider to represent the best embodimentthereof, but we desire to have it understood that the apparatus shownand described is only illustrative and that the invention may be carriedout by other means.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. Ap' aratus for producing a predetermined a rupt operating voltage forvoltage responsive devices in response to a voltage surge comprising apair of condensers, a high ohmic resistance connected between one set ofterminals of said condensers, said terminals being the supply terminalsof the voltage responsive device, a spark gap connected between theother set of terminals of said condensers, a direct current sourceconnected across said spark gap for charging said condensers to a highvoltage below the normal.

breakdown voltage of said spark gap, and means responsive to a voltagesurge for initiating a voltage breakdown and a discharge of thecondensers across said spark gap.

2. Ap aratus for producing a predetermined a rupt operating voltage forvoltage responsive devices in response to a voltage surge comprising apair of condensers, a high ohmic resistance connected between one set ofterminals of said condensers, said terminals being the supply terminalsof the voltage responsive device, a sphere ap connected between theother set of terminals of said condensers, said sphere gap including anintermediate conductor member, a direct current source connected acrosssaid sphere gap for charging said condensers to a high voltage below thenormal breakdown voltage of said sphere gap, means for normally excitingthe intermediate conductor member of said sphere gap to give it apotential gradient approximately half way between the potential gradientof the spheres as determined by the normal voltage charge on thecondensers, and means responsive to a voltage surge for altering thepotential gradient of said intermediate conductor member to initiate avoltage breakdown and a discharge of the condensers across the spheregap.

3. Apparatus for producing a predetermined abrupt operating voltage forvoltage responsive devices in response to abnormal surges on live highvoltage transmission lines comprising a pair of condensers, a high ohmicresistance connected between one set of terminals of said condensers,said terminals being the supply terminals of the volt age responsivedevice, a three electrode spark gap having two electrodes connectedbetween the other set of terminals of said condensers and anintermediate electrode connected to the high voltage transmission linethrough a capacitance potentiometer, a direct current source connectedin parallel to the condenser terminals with the spark gap electrodes forcharging said condensers to a high direct current voltage below thenormal breakdown voltage across the spark gap, the capacitancepotentiometer connection to the transmission line being such as tonormally impress a voltage on the intermediate electrode intermediatethe voltages on the other two electrodes such that an abnormal voltagesurge on the transmission line will initiate a voltage breakdown and adischarge of said condensers across said spark gap.

4. In combination with a cathode ray 0scillograph having a cathode, ananode and cathode ray sweep plates, means for energizing the same byabrupt operating voltages in response to a phenomenon to be recordedcomprising a capacitance havlng charging and discharging circuits, thecharging circuit including a high voltage direct current source and ahigh ohmic resistance and the discharging circuit including said highohmic resist ance and a spark gap ad usted for a breakdown voltagehigher than the voltage of said source, means responsive to thephenomenon to be recorded for initiatin a voltage breakdown and adischarge oi the capacitance across said spark gap, and connections forenergizing the previously mentioned electrodes and plates of theoscillograph from the voltage impressed across said resistance when saidbreakdown occurs.

5. In combination with a cathode ray oscillograph having a cathode, ananode, and cathode ray sweep plates, capacitance, means for normallycharging said capacitance to a high direct current potential, meansresponsive to a phenomenon to be recorded for thecharging saidcapacitance, circuits for 1mpressing the voltage charge of saidcapacitance between the cathode and anode of the oscillograph when thedischarge occurs, a sweep voltage circuit including a resistance and acondenser connected in parallel with the cathode and anode, saidresistance and condenser being proportioned to charge the condenser at asuitable rate to provide a satis- I sociated with the capacitancethrough which factory time axis when said discharge occurs, and circuitsfor impressing the voltage of said condenser across the sweep plates.

6. In combination with a cathode ray oscillograph having a cathode, ananode, and cathode ray sweep plates, means for energizing saidelectrodes and plates in response to a phenomenon to be recordedcomglrisirig irect pacitance normally charged to a gh current potentialmeans for abruptly dis- Y charging said capacitance in response to aphenomenon to be recorded, a high ohmic resistance through which thedischarge current of the capacitance iscaused to flow, connections forimpressing the voltage across said resistance between the anode andcathode of said oscillograph, a sweep voltagecirouit inand a condenserproportioned to gradually' charge the condenser when a high directcurrent voltage is impressed between cathode and anode, said sweepvoltage circuit includ-' ing means for preventing the discharge of saidcondenser through'said resistance, and circuits for impressing thevoltage of said condenser across the sweeping plates.

8. In combination with a cathode ray oscillograph having a cathode, acapacitance with means provided for charging it to a suitable potential,a dischar e circuit for the capacitance including a t ree-electrode gapwhich normally has a higher breakdown potential than the potential imressed on the capacitance, means for an alancing the three-electrode gapsothat it is caused to spark in response to a voltage surge, andcircuits for impressing the discharge potential of the condenser on thecathode of the oscillograph. a

9. In combination with a cathode ray oscillograph having a cathode andanode electrodes, apparatus for producing an abrupt operating voltagebetween said electrodes comprising a capacitance, means for normal- 1ymaintaining a charge upon said capacitance of sufiicient magnitude tooperate said oscillograph, a three-electrode spark gap assaidcapacitance is adapted to be discharged but which is normally adjustedto prevent such discharge, and means for disturbing such adjustment toproduce a'discharge in resgo'nse to some phenomenon to be recorded, ancircuits for impressing the dischar e voltage across said e ectrodeswhen the discharge occurs. 7

In witness whereof, we havehereunto'set our hands, this 22nd day of Jan., 1929.

'ELMER J. WADE.

WILLIAM J. RUDGE, n.

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